Relief valve system for a scraper apron

ABSTRACT

This invention relates to a Relief Valve System for a Scraper Apron that permits fluid transfer at a relatively slow rate from the rod end of the apron lift cylinder to the head end at a first relatively low pressure when raising the scraper bowl with the apron closed and its control at neutral, and that permits such fluid transfer only at a second much higher pressure when the bowl and the apron are being simultaneously manipulated to contain a full load of material in the bowl.

United States Patent 1191 Schexnayder .[111' 3,854,381 -[4s1 Dec. 17,1974

RELIEF VALVE SYSTEM FOR A SCRAPER APRON [75] Inventor: Lawrence F..Sche xnayder, Joliet, Ill. '[73] Assignee: Caterpillar Tractor C0,, Peoria, 111.

[22] Filed: Feb. 4, 1974 [21] Appl. No.: 439,216

[52] US. Cl. 91/414 [51] Int. Cl. F15b 11/16, FlSb 13/06 1 [58] Field of Search ..9l/411R,414

[56] References Cited UNITED STATES PATENTS I 2,831,466 4/1958 Stueland 91/414 X 3,115,716 12/1963 Hein et al.... ..91/4l4X 12/1964 Koons..- 91/414 X 3,324,882 6/1967 Keir 91/414 X Primary ExaminerEdgar W. Geoghegan Attorney, Agent, or Firm-Wegner, Stellman, McCord, Wiles & Wood 5 7 ABSTRACT This invention relates 'to a Relief Valve System fora Scraper Apron that permits fluid transfer at a relatively slow rate from the rod end of the apron lift cylinder to the head end at a first relatively low pressure vwhen raising the scraper bowl with the apron closed and its control at neutral, and that permits such fluid transfer only at a second much higher pressure when the bowl and the apron are being simultaneously manipulated to contain a full load of material in the bowl.

. 7 Claims, 2 Drawing Figures PATENTEL SEC 1 71974 sum 10F '2 PATENTELBFII H914 3.854.381

sum 2 nr 2 1 Q RELIEF VALVE SYSTEM FOR A SCRAPER APRON BACKGROUND OF THE INVENTION Operating conditions encountered in the use of scrapers that have a bowl and apron make it desirable to have three hydraulic pressure relief systems that function in different ways at different pressures and at different rates of flow. Such scrapers conventionally utilize a control valve system including a bowl control spool valve and a scraper control spool valve in an open center hydraulic circuit. The operating conditions are as follows:

a. When supplying fluid to either end of the bowl lift cylinders or the apron lift cylinder, a relief valve is needed to limit the maximum pressure supplied thereto.

b. When the bowl is being lifted with the apron in its neutral or holding mode of operation, pressure at the rod end of the apron lift cylinder must be relieved because the geometry of the scraper bowl pivot connections is such that the pivot connections of the apron cylinder and of the apron piston are mechanically forced apart, thus putting pressure on the apron cylinder rod end conduit.

c. There are relatively infrequent operating circumstances which occur, for example, when cyclically manipulating both the bowl raising and apron lowering control spools in order to fully contain loose material in the bowl at the end of a loading operation.

SUMMARY OF THE INVENTION The first condition above described-is provided'for in all hydraulic control circuits for scrapers, and the need is met by incorporating into the hydraulic control sysgooseneck frame. An apron 26 is rockably connected tem a conventional high flow capacity (typically 80 gallons per minute) pressure relief valve which opens at about 2,000 psi.

The present invention is concerned with the provision of a novel arrangement for handling relief of pressure from the rod end of the apron lift cylinder under the second and third conditions described above.

The conduits which supply fluid to or vent fluid from the head end and the rod end of the apron lift cylinder are connected with a dual pressure setting poppet relief valve that has the poppet carried in a load piston. When the poppet valve is open, fluid from the rod end of the apron lift cylinder is passed to the conduit for the head end of the apron lift cylinder. A signal'pressure from the apron control spool'valve is applied to the loadpiston, so that when the apron spool valve is in neutral position the load piston is not subjected to fluid pressure because the apron spool valve passages are open to the reservoir. Under such conditions the poppet can open about at 1,000 psi. On the other hand, when the apron control valve is in the apron loweringmode the load piston is subjected to substantial signal pressure from the apron circuit which forces the load cylinder up and thereby increases the pressure required to open the v poppet valve to about 2200 psi.

1. Pressure relief at the rod end of the apron lift cylinder when the bowl is being raised with the apron control in neutral position extends the service life of the components and reduces the horsepower required to a sufficient apron closing force is obtained for load re-- tention purposes.

3. The low flow capacity of the poppet valve and transfer of fluid from the rod end to the head end of the apron lift cylinder is more advantageous under both of the above described conditions than would be a return of fluid from the rod end through a return conduit to the fluid reservoir.

THE DRAWINGS FIG. 1 is a side elevational view of a tractor-drawn two wheel scraper; and FIG. 2 is'avhydraulic control circuit diagram.

DETAILED DESCRIPTION OF THE INVENTION I In FIG. 1, a conventional two wheel scraper is illustrated at as drawnby a tractor 11 through a hitch connection generally indicated at 12. A bowl 13 is raised or lowered around a pivot connection 14 which is associated with'the rear scraper wheels 15 by a pair of bowl lift cylinders 16 which are pivotally suspended from a gooseneck frame 17 at 18 and which have piston rods 19 pivotally connected to the bowl at 20. Apair of draft arms 23 are connected to opposite sides of the bowl at pivots 24 and extend forwardly to be secured to a cross tube 25 which is integrally attached to the to the opposite sides of the bowl at pivot connections 27, and is raised or lowered for opening and closing the forward portion of the bowl by a centrally mounted apron lift cylinder 28. The apron lift cylinder has a lower pivotal connection 29 to the cross tube 25, and

has a piston rod 30 with an upper pivotal connection 31 to a lever 32 which has its forward e'nd'pivotally mounted on the gooseneck frame 17 at'33. At the rear of the lever 32 is a pivot 34 for an apron lift link 35 which has its lower end connected to the apron 26 by a pivot 36. Further, an ejector 37 which isdisposed within the bowl may be moved forwardly to discharge the contents in a well-known manner.

A control valve assembly 40 which controls the flow of fluid to and from the bowl lift cylinders 16 and the apron lift cylinder 28 is mounted on the tractor 11 as are also a bowl lift control lever 41 and an apron lift control lever 42,-whichactuate the control valve assembly. As seen in FIG. 2, a housing 44 of the control valve assembly includes a bowl valve -bore 45 and an apron valve bore 46 which'carry, respectively, a bowl lift spool 47 and an apron lift spool 48 for respectively controlling the bowl lift cylinders 16 and the apron lift cylinder 28. The upper end of each spool is connected through a linkage (not shown) to the appropriate con: trol lever 41 or 42. Conventional centering spring assemblies 49 and 50 are disposed on the lower ends of the, spools to normally retain the spools in 'a central or neutral (N) position.

A hydraulic pump 53 delivers fluid under pressure from a'reservoir 54 through a conduit '55 man inlet passage 56 in the control valve assembly 40; and when the spools 47 and 48 are both in the illustrated (N) position the fluid passes from the inlet passage 56 through an apron valve inlet passage 57, a return passage 58, and a drain conduit 59 to the reservoir 54. A relatively high flow capacity relief valve 60 which communicates with the inlet conduit 55 opens at 2,000 psi. to return fluid from the inlet conduit to the reservoir at a relatively high flow rate such as 80 gallons per minute.

Manipulation of the bowl lift control lever 41 to lower the bowl 13 moves the bowl lift spool 47 upwardly to the lower (L) position so that pressurized fluid is delivered from the inlet passage 56 through an annulus 61 and downwardly through the bore 45 into an annulus 62 to a first bowl cylinder conduit 63 that is connected to the head ends of the bowl lift cylinders 16 to extend the piston rods 19. Conversely, downward movement of the bowl lift spool 47 to the raised (R) position allows fluid to be delivered from the inlet passage 56 to an annulus 64 and upwardly through the bore 45 and an annulus 65 to a second bowl cylinder conduit 66 that connects with the rod ends of the bowl lift cylinders 16.

When the bowl lift spool 47 is in the (L) position to apply pressure to the head ends of the cylinders 16, fluid from the rod ends flows reversely through the conduit 66, upwardly through the bore 45, and through an upper end annulus 67 to the return conduit 59. Conversely, when the spool 47 is in the (R) position, fluid flows reversely through the conduit 63, downwardly through the bore 45, and through a lower end annulus 68 to the return conduit 59.

In a like manner when the apron lift spool 48 is moved upwardly to the lowering (L) mode of operation, the inlet passage 57 is communicated with annuli 73 and 74 via the bore 46 and thence to'a first apron cylinder conduit 75 leading to the rod end of the apron lift cylinder 28. When the apron spool 48 is moved downwardly to the apron raising (R) mode of operation, the inlet passage 57 is communicated with the annuli 76 and 77 via the bore 46 and to a second apron cylinder conduit 78leading to the head end of the apron lift cylinder. Upper and lower end annuli 79 and 80 communicating with the apron spool bore 46 also open onto the return passage 58 and the return conduit 59 in order to return fluid from the low pressure end of the lift cylinder back to the reservoir 54.

As heretofore described the bowl lift cylinder control and the apron lift cylinder control are conventional. The novel structure and operation of the present invention will now be described.

The present invention includes a dual pressure setting relief valve 85 adapted to relieve excess pressure in the rod end conduit 75 associated with the apron lift cylinder 28 by transferring it to the head end conduit 78. Such dual pressure relief valve includes a housing 86 with an inlet passage 87 opening on the apron lift cylinder rod end conduit 75 and communicating with an outlet passage, 88 opening on the head end conduit 78 through a poppet relief valve 89. The poppet valve is longitudinally aligned with a bore 90 in the housing in which a load piston 91 is slideably mounted. The load piston 91 is contained in the bore 90 by a sealed threaded end plug 92 and is provided with longitudinal grooves 93 which are open toward the plug end of the load piston and sealed at their upper ends by a shoulder 93A. The grooves 93 open on a passage 94 that communicates with a signal conduit 95 to permitthe pressure in the apron valve inlet passage 57 to be applied against the load piston. The load piston also has an in- I ternal blind bore 96 in which a poppet valve loading compression spring 97 is mounted, so the load piston provides a movable spring seat, and the poppet valve 89includes a conical head portion 98 and a reduced diameter cylindrical spring guide 99 defining a shoulder 100 against which the spring 97 bears to biasably load the poppet valve so that the conical head portion is disposed against an annular seat 101 within the hous- %Vhen supplying fluid to the ends of either the bowl lift cylinders 16 or apron lift cylinder 28 by movement of a single one of the spools 47 or 48, the inlet conduit is pressurized and reflects the maximum pressure in the system aslimited in the usualmanner by the main relief valve which has a flow capacity of approximately gallons per minute. However, when the apron lift control spool 48 is disposed in neutral, as shown, both the rod end conduit 75 and head end conduit 78 associated with the apron lift cylinder 28 are thereby blocked. Consequently, when the bowl 13 is raised by manipulating the bowl lift control spool 47 and directing fluid to the rod end conduit 66, the geometry of the various pivotal connections imposes a force on the closed apron at the end of the scraper loading cycle and a force on the opposite pivotal connections 29 and 31 tending to extend the piston rod 30 of the apron lift cylinder. Such force results in 'pressurizing the rod end of the apron lift cylinder, which is reflected in the rod end conduit-75 and inlet passage 87 of the dual pressure relief valve which is set to open at a relatively lower pressure. This is so because the signal conduit leading to the load piston 91 is open back to the reservoir 54 via the inlet passage 57 and return passage 58. The load piston thus remains in the position shown and the spring 97 imposes only a relatively light load against the poppet valve 89. Such poppet valve,

under these conditions is set to open at approximately 4 bowl 13, such as by cyclically moving the spool 47 intermediate the raising and neutral modes and moving the spool 48 to the lowering mode, it is desirable to allow a relatively high pressure in the rod end of the f fluid pressure in the inlet passage 57, isolated from the return conduit 58, is communicated by the signal conduit '95 and grooves 93 to act against the load piston 91 in the dual pressure relief valve 85. This moves the load piston upwardly against a shoulder 102 which is a short distance below the valve seat 101, and compresses the spring 97 against the poppet valve 89 to establish a second, higher pressure for relief purposes (e.g., 2,200 psi). Since the flow capacity of this relief valve is lower than relief valve 60, its relief pressure setting is established at a value something greater than relief valve 60 to assure that when they are both incommunication with the rod end of the apron lift cylinder 28 the relief valve 60 will handle the majority of the flow and serve as the main relief for the system.

tions should be understood therefrom, as modifications will be obvious to those skilled in the art.

I claim:

1. In a hydraulic system for controlling the bowl and apron of a scraper, which system includes a bowl lift cylinder, an apron lift cylinder, a bowl control spool valve connected by bowl cylinder conduits to the head end and to the rod end of said bowl lift cylinder and controlling admission of hydraulic fluid to said conduits; an apron control spool valve connected by apron cylinder conduits to the head end and to the rod end of said apron lift cylinder and controlling admission of hydraulic fluid to said apron cylinder conduits, and a high flow ratepressure relief valve for returning hydraulic fluid from said system to a reservoir, pressure relief means for the rod end of the apron lift cylinder comprising, in combination:

a relief valve housing that has an inlet passage connected to the apron cylinder conduit for the rod end of the apron lift cylinder and an outlet passage;

a valve member in said housing that controls the passage of hydraulic fluid from the inlet passage to the outlet passage;

means biasing said valve member to a closed position a second, and higher predetermined pressure to open said valve member.

2. The pressure relief means of claim 1 in which the outlet passage of the relief valve housing communicates with the apron cylinder conduit for the head end of the cylinder.

3, The pressure relief means of claim -1 in which the inlet and outlet passages in the relief valve housing are dimensioned to pass fluid only at a rate which is substantially less than the rate at which fluid passes through the high flow rate pressure relief valve.

4. The pressure relief means of claim 1 in which the means biasing the valve member to a closed position comprises a compression spring, and the means for increasing the force applied to the valve member comprises a movable spring seat which compresses said spring in response to increased pressure in the signal conduit.

5. The pressure relief means of claim 4 in which the valve member is a poppet valve, the movable spring seat is a load piston, slideable in a bore in the housing, in which the spring and the poppet valve are carried, and in which the signal conduit communicates with the housing to apply fluid pressure to move the load piston toward the poppet valve.

6. The pressure relief means of claim 5 in which the load piston has external passage means which faces away from the poppet valve, and the pressure of fluidin the signal conduit communicates through said external passage means to bear against said load piston.

7. The pressure relief means of claim 6 in which the tially spaced grooves in the surface =I of the load piston. 

1. In a hydraulic system for controlling the bowl and apron of a scraper, which system includes a bowl lift cylinder, an apron lift cylinder, a bowl control spool valve connected by bowl cylinder conduits to the head end and to the rod end of said bowl lift cylinder and controlling admission of hydraulic fluid to said conduits; an apron control spool valve connected by apron cylinder conduits to the head end and to the rod end of said apron lift cylinder and controlling admission of hydraulic fluid to said apron cylinder conduits, and a high flow rate pressure relief valve for returning hydraulic fluid from said system to a reservoir, pressure relief means for the rod end of the apron lift cylinder comprising, in combination: a relief valve housing that has an inlet passage connected to the apron cylinder conduit for the rod end of the apron lift cylinder and an outlet passage; a valve member in said housing that controls the passage of hydraulic fluid from the inlet passage to the outlet passage; means biasing said valve member to a closed position with a predetermined force so that a first predetermined pressure in the inlet passage is required to open said valve; a signaL conduit connecting said housing to the apron control spool valve; and means responsive to increased pressure in said conduit to increase the force applied to said valve member by the biasing means and thereby require a second, and higher predetermined pressure to open said valve member.
 2. The pressure relief means of claim 1 in which the outlet passage of the relief valve housing communicates with the apron cylinder conduit for the head end of the cylinder.
 3. The pressure relief means of claim 1 in which the inlet and outlet passages in the relief valve housing are dimensioned to pass fluid only at a rate which is substantially less than the rate at which fluid passes through the high flow rate pressure relief valve.
 4. The pressure relief means of claim 1 in which the means biasing the valve member to a closed position comprises a compression spring, and the means for increasing the force applied to the valve member comprises a movable spring seat which compresses said spring in response to increased pressure in the signal conduit.
 5. The pressure relief means of claim 4 in which the valve member is a poppet valve, the movable spring seat is a load piston, slideable in a bore in the housing, in which the spring and the poppet valve are carried, and in which the signal conduit communicates with the housing to apply fluid pressure to move the load piston toward the poppet valve.
 6. The pressure relief means of claim 5 in which the load piston has external passage means which faces away from the poppet valve, and the pressure of fluid in the signal conduit communicates through said external passage means to bear against said load piston.
 7. The pressure relief means of claim 6 in which the external passage means are a plurality of circumferentially spaced grooves in the surface of the load piston. 